selftests: KVM: Add OSLSR_EL1 to the list of blessed regs

OSLSR_EL1 is now part of the visible system register state. Add it to
the get-reg-list selftest to ensure we keep it that way.

Signed-off-by: Oliver Upton <oupton@google.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20220203174159.2887882-6-oupton@google.com